SynergismofnaturalandconstructedwetlandsinBeijingC

EcologicalEngineering37(2011)128–138ContentslistsavailableatScienceDirectEcologicalEngineeringjournalhomepage:∗,JianmingHongb,1,KejiangZhangcaSchoolofEnvironment,BeijingNormalUniversity,StateKeyJointLaboratoryofEnvironmentalSimulationandPollutionControl,Beijing100875,ChinabCollegeofLifeSciences,CapitalNormalUniversity,Beijing100048,ChinacDepartmentofCivilEngineering,UniversityofCalgary,Alberta,CanadaT2N1N4articleinfoArticlehistory:Received17January2010Receivedinrevisedform4August2010Accepted7August2010Availableonline24September2010Keywords:IntegratedwetlandsystemConstructedwetlandsNaturalwetlandsNetwaterlossWaterenvironmentalcapacityabstractAnintegratedwetlandsystem(IWS)includingconstructedwetlands(CWs)andmodifiednaturalwetlands(NWs)forwastewatertreatmenttoreplenishwatertowetlandslocatedattheBeijingWetlandSchool(BWS)inBeijing,China,ispresentedinthispaper.ThesynergisticeffectsofCWsandNWsontreatedwaterqualityareinvestigated.TheIWSisprovedtobeaneffectivewastewatertreatmenttechniqueandabetteralternativetoalleviatethewatershortageforconservationofwetlandsbasedonthemonitoringdataobtainedfromOctober2007to2008.TheresultsshowthatCWsandNWsplaydifferentrolesinremovingcontaminantsfromwastewater.TheCODremovalefficiencyinCWsishigherthanthatinmodifiedNWs,whereasthemodifiedNWscancompensateforthedeficiencyofCWswhereastableandsufficientrhizosphereisnotfullyformedinthestart-upperiod.AllremovalratesofCOD,TN,andTPinCWsandmodifiedNWsvaryfrom50to70%,whilethetotalremovalrateofCOD,TN,andTPinIWSisabout85–90%.TheoperationalresultsshowthatthemaximumarealoadingoforganicpollutantsinmodifiedNWs(65kg/had)isslightlyhigherthantheempiricalone(60kg/had)recommendedbyUSEPA(2000)forfreewatersurfacewetlands.©2010ElsevierB.V.Allrightsreserved.1.IntroductionWetlandsarefewerinBeijingduetounbalancedspatialdis-tributionofwaterresourcescomparedwithothercities,suchasShanghaiandWuhaninChina(Zhaoetal.,2005,2006;Gongetal.,2007;Xuetal.,2010).Theselimitedwetlandsarefacingincreas-ingdegradationduetowatershortageandpollution.Inordertoconserveexistingwetlandsandalleviatethedegradationofwet-lands,thetreateddomesticandagriculturalwastewatercanbeconsideredwatersourcestoreplenishwatertowetlands(Riosetal.,2009).However,conventionalwastewatertreatmentplantsinmostruralareasofBeijingarenotavailableduetotheirhighcostsforconstructionandoperation(Chenetal.,2008).Constructedwetlands(CWs),whichareecologicallyengineeredsystemandakintonaturalwetlands(NWs),arewidelyusedasacost-effectiveapproachfordifferentkindsofwastewatertreat-ment(MitschandJorgensen,1989;Sunetal.,2005;ProchaskaandZouboulis,2006;EkeandScholz,2008).Manysuccessfulprac-ticesinUSA,Finland,Italy,NewZealand,BelgiumandPolandhavebeenpresentedinliterature(KernandIdler,1999;Newmanet∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddresses:[e-mail],[e-mail](B.Cui),[e-mail](J.Hong).1Tel.:[phone];fax:[phone].al.,1999;Schaafsmaetal.,1999;Knightetal.,2000;Nguyen,2000;Koskiahoetal.,2003;Mantovietal.,2003;Poachetal.,2003;Rousseauetal.,2004a;TuszynskaandObarska-Pempkowiak,2008).However,alargenumberofreportsemphasizetheremovalefficiencyofpollutantsornutrientsinCWswhileignoringthefactthatCWsoftenneedlargeareasoflandandalongerreten-tiontimetoachieveacceptableeffluentwaterquality(AkratosandTsihrintzis,2007).Ontheotherhand,CWshaverelativelyloworunstableperformanceinthestart-upperiodduetoimmaturerhi-zosphereenvironments(Vymazaletal.,1998).AlthoughCWscansimulateandenhancesomefunctionsofNWs,theycannotcom-pletelyreplaceNWsintheremovalofpollutantsduetoalackofdiversifiedplantcommunities,maturemicrobialcommunities,andstablerhizosphereenvironments.ThehistoryofNWsforwastewatertreatmentcanbetracedbackto1912(KadlecandKnight,1996).Sincethen,wetlandshavebeenconsideredalternativesforwastewatertreatmentduetotheirapparenttreatmentcapacities.ManyNWs,suchasriparianwetlands,areusedtoreducethenutrientloadofthrough-flowingwaterbyremovingnitratesandphosphorusfromsurfaceandsubsurfacerunoff(Zedler,2003;Hoganetal.,2004;HoganandWalbridge,2007).However,someproblemsofNWsarealsoobvi-ous,suchaslowercontaminantloadandlimitedself-purifyingcapacities.Itisassumedthatanintegratedwetlandsystem(IWS)com-posedofCWsandNWsbasedontheprincipleofcomplementary0925-8574/$–seefrontmatter©2010ElsevierB.V.Allrightsreserved.doi:10.1016/j.ecoleng.2010.08.001H.Zhangetal./EcologicalEngineering37(2011)128–138129Fig.1.Decisionsupporttreeforthedesignoftheoptimumcombinationofconstructedwetlandsandmodifiednaturalwetlands.advantagescanachievegreatertreatmentcapacitythananyindi-vidualsystem.Thus,howtodesignandoperatethesynergisticsystemofCWsandNWswillbeafocusinwaterqualityimprove-ment(MitschandGosselink,2000;ZedlerandKercher,2005;Verhoevenetal.,2006).Inthispaper,anIWSisappliedtopurifythedomesticwastewaterdischargedfromthestudentdormitories.TreatedwaterwillberechargedtowetlandsattheBeijingWet-landSchool(BWS).Theobjectivesofthispaperareto(